The present invention relates to a full injection pump in general, and more particularly to a distributor type fuel injection pump for injecting high pressure fuel into combustion chambers of an internal combustion engine.
One of the known fuel injection pumps of the type under discussion is disclosed in U.S. Pat. No. 4,449,504. In this known fuel injection pump, the valve-closing member is formed as a cylindrical reciprocating piston which is tightly guided in the cylindrical bore which opens into the pump working chamber. The fuel-unloading chamber is opened, during the idle mode of operation of the internal combustion engine by an electrically-pneumatically operated valve, towards the second unloading conduit or passage, so that the reciprocating piston can be adjusted, due to the pressure prevailing in the pump working chamber during the advancement of the pump piston, by a predetermined path defined by the pre-stressing of the restoring spring and by a stop. Thereby the pumping rate during the idle mode of operation is reduced while the fuel injection is not, however interrupted. Such devices serve to make smoother the combustion process, with the fuel injection pumps operated with low speeds. The second unloading passage is either continually opened during the idle mode of operation or is continually closed during a partial or full loading of the engine.
Also known is a device including injection nozzles. Such a device has been disclosed in DE-OS No. 33 00 876. These nozzles provide a preliminary fuel injection. There preliminary injection devices have the disadvantage that the preliminary injection must be carried out before the main injection and the additional devices to enable such a preliminary injection are rather expressive and require throttles which strongly throttle the fuel when the speed rises. In addition, the preliminary injection is strongly changed with dynamic operation ratios.
A further disadvantage of conventional devices resides in that the fuel pumps do not ensure unloading in all load ranges.